Update README testing section
Update README testing section

Solidus is now available to the public. Don't need work around for
testing.

solidusio/solidus_auth_devise,solidusio/solidus_auth_devise,AngelChaos26/mandrill,mayankdedhia/solidus_auth_devise,mayankdedhia/solidus_auth_devise,AngelChaos26/mandrill,mayankdedhia/solidus_auth_devise,AngelChaos26/mandrill,solidusio/solidus_auth_devise